Japanese Utility Model Laid-open No. SHO 64-13740 describes a semiconductor device in which each lead element is secured to a copper-containing pad in each output terminal region. The copper-containing pad enables the lead element to be strongly affixed to the pad by conventional soldering. The copper-containing pad is formed by screen-printing a copper paste which is then hardened by the application of heat.
FIG. 1 shows a photovoltaic apparatus output terminal structures which include copper-containing pads. In each output terminal region, the output terminal structure comprises, in order, an insulating substrate 210, a conductive belt 220, a metal layer 230, an amorphous silicon layer 240, a transparent conductive layer 250, an output terminal 260, a copper-containing pad 270 and a lead element 280.
The insulating substrate 210 is generally rectangular and is often made of polyimide and the like. The conductive belt 220 is disposed along one side edge of the insulating substrate 210, and is formed by screen-printing a metal paste onto the substrate and, then hardening the metal paste by heating. The output terminal 260 is of generally the same shape and the same material as the conductive belt 220 and is formed on the transparent conductive layer 250. The copper-containing pad 270 is generally rectangular, and is formed on and around one edge of the output terminal 260. The lead element 280 is made of a metal strip and is soldered to the copper-containing pad 270.
When the lead element 280 is pulled, the lead element 280 can inadvertently be readily removed as shown in FIG. 2. Because the adhesion between the insulating substrate 210 made of polyimide and the conductive belt 220 is generally weak, they will often separate easily.
On the other hand, even if the metal layer 230 is directly formed on the insulating substrate 210 without the conductive belt 220, the adhesion between the insulating substrate 210 and the metal layer 230 is also generally weak. Therefore, when the lead element 280 is pulled, the lead element 280 can still be easily removed.
U.S. Pat. No. 5,133,810 describes another output terminal structure of a photovoltaic apparatus having an output terminal. In the output terminal structure, a lead element is connected to the output terminal, and a protective film is formed on the photovoltaic apparatus including the output terminal.
FIG. 3 shows another output terminal structure. It is noted that the same numerals represent corresponding elements shown in FIG. 1, and the explanation concerning these corresponding elements is omitted. In each such output terminal structure, a protective film 290 covers the output terminal region including a lead element 280. In such output terminal structures, because the protective film 290 covers the lead element 280, it is more difficult to inadvertently separate the lead element 280 from the terminal structure. However, spaces 300 are often formed at both sides along the lead element 280. As a result, moisture can advance into the interior of the photovoltaic apparatus through the spaces 300. Consequently, corrosion can occur, decreasing long term reliability.
There are other disadvantages. For example, the above described output terminal structure is not readily adapted to fabrication processes in which a plurality of photovoltaic apparatuses are divided from one large substrate. More specifically, if each of the lead elements of the output terminals of a plurality of photovoltaic apparatuses were covered with one protective film formed over the entire surface of all the photovoltaic apparatuses of the substrate, while one end portion of the lead element of each of the output terminals could be connected to the appropriate output terminal, the opposite end portion of the lead element might be located undesirably over another photovoltaic apparatus under the protective film.